The invention relates to an offset regulation device for a sensor module, in particular for acceleration sensors and pressure sensors, wherein the offset regulation device detects an actual value, compares this value to a desired value and, if there is a deviation, adjusts the actual value to match the desired value.
Various sensor modules with offset regulation are known. With these, zero point changes are measured, which are also referred to as offset drift, and are compensated with the aid of a control circuit. These changes can occur on the most varied components, particularly the actual sensor element that functions to detect a physical variable, as well as the connections between sensor element and signal processing unit. The causes for the offset drifts can be found, for example, in the aging of the components and the connections or they can be caused by temperature changes, which influence the properties of the components and their connections. Such influences can be omitted with the offset regulation in that a zero-point compensation takes place, so that the measuring result is not distorted owing to a displacement of the zero point. Many offset regulation devices are designed as high-pass filters, which filter out time-constant variables such as the zero point displacement of a signal.
However, the disadvantage of the offset regulation device is that impermissible changes in the zero point, caused by defective parts, e.g., parts that wear out too soon or age too fast or display an above-average temperature sensitivity, cannot be detected. The high-pass filter does not recognize whether the time-constant variable exceeds a specific maximum value or minimum value. In the event that the offset representing a zero point displacement exceeds a maximum or minimum permissible value, this is an indicator that a component is no longer operative. Exact measurements are no longer possible with an inoperative component because the behavior of these components changes so drastically that a reproducibility of the measuring result is no longer ensured. The measuring results obtained despite the offset regulation are incorrect. This is the case even if bonding connections age at different rates and short-circuits occur.
It is the object of the invention to correct these disadvantages with an offset regulation device of the initially mentioned type.
The above object generally is achieved according to the invention by an offset regulation device for a sensor module, in particular for acceleration sensors and pressure sensors, wherein the offset regulation device detects an actual value, compares this value to a desired value and, in case of a deviation, adjusts the actual value to the desired value, and wherein the offset regulation device includes a monitoring unit or device for recognizing an excessively high offset. The monitoring device comprises an analog or digital, clocked adder, wherein the monitoring device adds up the deviation between actual value and desired value, which has been weighted with an optional factor, and generates an error message once a maximum or minimum limit value has been reached.
Additional advantageous modifications follow from the description. For an offset regulation of the type disclosed herein, each fed-in value is weighted in the adder with a fixed constant, thereby resulting in a predetermination of the speed with which the minimum for maximum limit value is reached.
As a result of this, it is prevented that actually occurring errors, which are otherwise camouflaged, for example, by the high-pass effect of the offset regulation device, are recognized. It is an advantage in this case that the offset monitoring occurs during the offset regulation and errors can therefore be recognized directly during the measuring operation.
The invention is to be represented and explained in the following with the aid of an exemplary embodiment and in connection with the single Figure.